If you mean "Sweetheart" in the sense of two people who are married, dating, or courting:
Geliebter (געליבטער) = male sweetheart
Geliebte (געליבטע) = female sweetheart
In general:
"Zissele" and "Ziskeit" mean "Sweetness," and "Zisseh neshomeh" means "Sweet soul," while "Neshomeleh" means something like "Dear soul"; those are all terms of endearment.
"Sweetheart" would literally be "Zisseh hartz," but that's not a term of endearment that I have ever heard.
Vugglemantis
Bubula is a Yiddish word usually used by grandmothers or older people. Bubula usually refers to children. In modern times, the word is used to reference anyone who is considered close. The meaning for this traditional Yiddish word is similar to "dear" or "sweetheart."
Bling is not a Yiddish word or a Hebrew word.
The Yiddish word for Yiddish is "Yidish" (יידיש).
The Latin word for sweetheart is puella. The word sweetheart in Spanish is novio, in Italian it is Tesoro, and in French it is amoureux.
The Yiddish word for darkness is "dunkel."
It is the Yiddish word for a woman who is not Jewish. It is slang in English, but it is not slang in Yiddish.
The word 'sweetheart' in Indonesian is sayang.
The Yiddish word for expert is "experte" (אַקספּערטע).
The Yiddish word for grandfather is "zeide" or "zayde."
One word for knickknacks in Yiddish is "tchotchkes".
The Yiddish word for disappointed is "Ahntoisht".